There is no single correct time. Blanch duration in water at 90 to 100 degrees Celsius runs from roughly 30 seconds for chopped spinach to 3 to 5 minutes for dense diced roots, and the correct figure for a given product is whatever the plant has validated for its own equipment, piece size and throughput. Time is an operating parameter, not the specification.
Indicative water-blanch windows used in industry are 1 to 2 minutes for green peas, 1.5 to 3 minutes for cut green beans, 2 to 3 minutes for broccoli and cauliflower florets, 2 to 4 minutes for sweet corn kernels, 30 to 60 seconds for chopped spinach and 3 to 5 minutes for beetroot or carrot dice. Steam blanching generally runs longer than water blanching for the same product because heat transfer is slower.
Four variables move those numbers, and all four change between plants. Piece size and geometry decide how long heat takes to reach the thermal centre. Water or steam temperature sets the driving force. Belt loading changes the effective temperature the product sees, because a heavily loaded belt cools the bath locally. And crop maturity changes the starting enzyme load.
The specification should therefore state the outcome rather than the clock. The standard outcome test is enzyme inactivation, most commonly a negative peroxidase result, sometimes lipoxygenase for peas and beans, taken on product after cooling. Peroxidase is heat-resistant, so its absence indicates the other quality-relevant enzymes are also inactivated.
Under-blanching leaves residual enzyme activity, which produces off-flavours, colour loss and texture change during frozen storage, typically appearing at three to six months rather than immediately. Over-blanching costs texture, leaches nutrients and colour into the blanch water, and reduces yield.
Ask the supplier for the validation report and the routine monitoring records, as set out in the blanching validation guide, rather than asking for a number you can put in a contract clause. A time copied from one plant into another plant’s specification is a clause that cannot be met and should not be enforced.